Table of Contents

Why is Reducing Pathogens Important?

Manure and improperly composted manure can be a source of pathogen
contamination on crop products intended for human consumption. Pathogens
have the potential to cause human illness when consumers are exposed
to them.

Good agricultural practices frequently suggest that uncomposted
manure should only be applied when the interval between application
and harvest is greater than four months.

Composting of manure kills most pathogens and greatly reduces the
risk of pathogen contamination.

What Pathogens?

Livestock and poultry manures naturally contain a wide range of
bacteria, viruses and protozoa. Some of these are known for their
adverse effects on people. Bacteria known to be human pathogens
include certain strains of E. coli, including 0157:H7,
Salmonella spp., Listeria, Streptococcus
spp., Campylobacter, Clostridium spp. Protozoa
include Giardia and Cryptosporidium. Most viruses
found in animal manure do not infect humans.

The levels of these pathogens in manure can vary and depend partially
on the livestock species. Generic E. coli can be found
in the manure from all species. E. coli 0157:H7 is most
common in cattle manure but has also been found in the manure of
other mammals. Salmonella is most commonly found in poultry
manure.

Camplyobacter is common in poultry manure but can be found
in all species. Listeria is common in cattle and sheep
manure but may be found in all species. Cryptosporidium
are common in cattle manure (particularly young animals) but may
also be found in manure from pigs and sheep.

Occasionally food products are found to be contaminated with one
or more of these organisms. There are many sources of contamination
beyond improperly composted manure such as poor water quality, transmission
from improperly sanitized equipment and people handling produce
during processing (improper hand washing procedures) have been found
to be sources in some cases.

In addition to livestock sources of pathogens, there have been
studies to indicate that green yard wastes can be contaminated,
primarily due to pet droppings. These materials should be composted
and used with care in the planting of food crops.

How Long Do Pathogens Survive?

The survival of these pathogens in manure will largely depend on
the temperature and moisture content of the materials. Other factors
are oxygen level, pH, ammonium content, microbial competition, etc.
In general, the higher the temperature and the longer the storage
or treatment time of the manure, the less likely pathogens will
survive. Most pathogens have short survival times when under very
dry conditions.

The following table shows some reported survival times based on
materials temperatures or moistures as indicated.

Table 1. Potential Survival of Fecal Pathogens
in the Environment

Material

Duration of Survival

Cryptosporidium

Salmonella

Campylobacter

E. coli 0157:H7

Water - Frozen

>1 year

>6 months

2-8 weeks

>300 days

Water - Cold
(5ºC)

>1 year

>6 months

12 days

>300 days

Water -
Warm (30ºC)

10 weeks

>6 months

4 days

84 days

Soil -
Frozen

>1 year

>12 weeks

2-8 weeks

>300 days

Soil -
Cold (5ºC)

8 weeks

12-28 wks

2 weeks

100 days

Soil -
Warm (30ºC)

4 weeks

4 wks

1 week

2 days

Cattle
manure - Frozen

> 1 year

>6 months

2-8 weeks

>100 days

Cattle
manure - Cold (5ºC)

8 weeks

12-28 weeks

1-3 weeks

>100 days

Cattle
manure - Warm (30ºC)

4 weeks

4 weeks

1 week

10 days

Liquid manure

>1 year

13-75 days

>112 days

10-100 days

Composted manure

4 weeks

7-14 days

7 days

7 days

Dry surfaces

1 day

1-7 days

1 day

1 day

Source: Human and Animal Pathogens in Manure, Olsen, M. E.

Does Composting Help?

Using proper composting procedures can drastically reduce the number
of pathogens in manure. One of the parameters identified in many
composting procedures is to maintain temperature above 55ºC
for at least 3 days when using aerated or in-vessel systems. In
windrow systems, the core of the windrow may reach these temperatures,
but surface zones and near the base of the windrow will have lower
temperatures. Turning or mixing the windrow will introduce oxygen
to the windrow and quickly increase temperatures in the earlier
stages of composting. Turning with equipment that moves material
from the surface to the core of the windrow will expose more materials
to higher temperatures. Repeated turnings are necessary to ensure
all materials are exposed to at least 3 consecutive days of high
temperature.

It is generally recommended that windrows maintain a core temperature
of 55ºC for 15 days with at least 5 turnings. Due to the need
for proper mixing and consistent high temperatures, pathogen reduction
in windrow composting has sometimes been found to be less consistent
than when using well-managed, aerated static pile or in-vessel systems.

Some organisms are more difficult to kill than others and temperatures
must be regularly monitored to ensure that appropriate temperatures
are maintained. Proper moisture levels (50%-60%), optimum C:N ratios
(25:1-30:1) and appropriate aeration or turnings are all factors
to ensuring the conditions are optimum to reach and maintain the
necessary temperatures. Records should be kept for temperatures,
compost conditions, C:N ratio, moisture, and the date/time of turnings.

Clean the compost turning equipment between uses to avoid re-establishing
the pathogens in the compost. Equipment should not go from a new
compost pile to an established windrow without being cleaned as
it may carry pathogen contaminants from one pile to another. Loaders
used to handle fresh manure should be cleaned before handling compost.
Windrows should be turned with equipment that is capable of turning
the surface material into the middle of the windrow.

Compost Teas

Compost teas are made by putting a small quantity of mature compost
(in a perforated bag) into water and allowing it to steep (also
known as brewing). This creates a compost tea solution that can
be applied to the crop as a foliar source of nutrients. Some research
has also found suppression of certain plant diseases when applied
to crop foliage. Compost teas should only be made with fully mature
compost to reduce pathogens. Adding sugar or molasses materials
during the steeping process has been reported to increase the incidence
of pathogens in the compost tea. Compost tea must be aerated during
the "steeping" process and used immediately after steeping
to reduce the risk of pathogen contamination. Do not apply compost
teas to edible parts of the crop or apply near harvest time.

Manure tea is made using non-composted or improperly composted
manure and may contain high levels of pathogens. Do not apply manure
tea directly to crops. After field application, observe the appropriate
waiting periods before harvest of food crops (example: 4 months).

Summary

Composting is a useful strategy to reduce pathogens in manure but
care must be taken to correctly manage the composting process.

Cornell
Composting Homepage - Web site maintained by the Cornell Waste
Management Institute and provides access to a variety of composting
educational materials and programs developed at Cornell University,

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